Compositions for solution process, electronic devices fabricated using the same, and fabrication methods thereof

ABSTRACT

Exemplary embodiments provide compositions for a solution process, electronic devices fabricated using the same, and fabrication methods thereof. An oxide nano-structure is formed using a sol-gel process. An oxide thin film transistor is formed using the oxide nano-structure.

TECHNICAL FIELD

The disclosure herein relates to compositions for a solution process,electronic devices fabricated using the compositions, and fabricationmethods thereof. More particularly, the present disclosure hereinrelates to oxide nano-structures, oxide thin film transistors, oxidesemiconductor devices and fabrication methods thereof.

Oxide thin film transistors and methods of fabricating the same using asol-gel process have been proposed as one of national projects that areperformed by the Ministry of Education, Science and Technology and theKorea Science and Engineering Foundation [Project Ref No.: 2008-8-0878,Title of the Project: Technology Development to Solution Based Silicon(SBS) thin films for Next Generation Displays and to All Solution Based(ASB) Thin Film Transistors]

BACKGROUND ART

Recently, oxide thin films have been widely used in displays andsemiconductor devices. A zinc oxide (ZnO) material of the oxide thinfilms is a II-VI group compound semiconductor material having a directtransition characteristic. Further, the zinc oxide (ZnO) material hashigh band gap energy of about 3.37 electron volts (eV). Thus, the zincoxide (ZnO) material may be transparent to visible rays and may bewidely used in photo devices {see an article by D. C. Look et al.,entitled “Recent advances in ZnO material and devices”, Material Scienceand Engineering, B 80, 383 (2001)}.

The ZnO material may exhibit an N-type characteristic due tointerstitial zinc atoms and native defects (e.g., oxygen vacancies), andthe electrical resistivity of the ZnO material may vary within the rangeof about 1×10⁻² Ωcm to about 1×10¹⁰ Ωcm according to a processcondition. The ZnO material may be used as a transparent electrode bydoping the ZnO material with N-type impurities to increase the electronconcentration thereof. The N-type impurities may include III-groupelements or VII-group elements. For example, the typical III-groupelements may be gallium (Ga) atoms, aluminum (Al) atoms or indium (In)atoms. The ZnO material doped with gallium (Ga) atoms may be referred toas a gallium zinc oxide (GZO) material {see an article by Quan-Bao etal., entitled “Structural, electrical and optical properties oftransparent conductive ZnO:Ga films prepared by DC reactive magnetronsputtering”, Journal of Crystal Growth, 304, 64 (2007)}, and the ZnOmaterial doped with aluminum (Al) atoms may be referred to as analuminum zinc oxide (AZO) material {see an article by Byeong-Yun Oh etal., entitled “Properties of transparent conductive ZnO:Al filmsprepared by co-sputtering”, Journal of Crystal Growth, Volume 274, 453(2005)}. Further, the ZnO material doped with indium (In) atoms may bereferred to as an indium zinc oxide (IZO) material {see an article byLuna-Arredondo et al., entitled “Indium-doped ZnO thin films depositedby the sol-gel technique”, Thin Solid Films, 490, 132 (2005)}.

The above transparent conductive materials (e.g., transparentelectrodes) may be very attractive as candidates of the transparentindium tin oxide (ITO) material well known in the art.

The transparency of the zinc oxide material may provide the possibilityof fabrication of transparent transistors. Further, the zinc oxidematerial may be suitable for an active layer of the thin filmtransistors since the zinc oxide material provides a high mobility ofcarriers. The zinc oxide material may exhibit an excellent carriermobility of about 200 cm²/Vs in a bulk region thereof {see an article byD. C. Look et al., entitled “Electrical properties of bulk ZnO”, SolidState Commun., 105, 399 (1998)}. In addition, zinc compound materialsmay be formed by an ionic bond. Thus, a difference between the mobilityof the crystalline zinc compound material and the mobility of theamorphous zinc compound material may be relatively less as compared witha silicon material. Thus, the zinc oxide material may be very suitablefor the display devices that require the active layer having a highmobility. Furthermore, a zinc alloy material including the zinc compoundmaterial and other elements has been proposed to obtain high mobilityand stability in the active layer. For example, at least one ofmaterials (e.g., indium, tin and thallium) having an orbital 5 s or thehigher orbital (e.g., having a greater ion radius than zinc) may beadded to the zinc compound material, thereby forming the zinc alloymaterial such as an indium-gallium-zinc oxide (In—Ga—ZnO; IGZO)material, an indium-zinc oxide (In—ZnO; IZO) material, a tin-zinc oxide(Sn—ZnO; SZO) material, a tin-gallium-zinc oxide (Sn—Ga—ZnO; SGZO)material, an indium-tin-zinc oxide (In—Sn—ZnO; ISZO) material, athallium-zinc oxide (Tl—ZnO; TZO) material or a thallium-gallium-zincoxide (Tl—Ga—ZnO; TGZO) material. These zinc alloy materials have agreater positive ion than the zinc material. That is, the number ofperipheral electrons of the alloy materials may be greater than that ofperipheral electrons of the zinc material. The peripheral electrons maycontribute to the electron mobility. Thus, the electron mobility of thezinc alloy materials may be greater than that of the zinc material. Thegallium atoms in the zinc alloy materials (e.g., active layers) maycontrol the electrical characteristics thereof and may improve stabilitythereof. Recently, a study on the IGZO material has been increasinglydemanded to apply the IGZO material to the display devices. The IGZOmaterial may be formed using a pulsed laser deposition (PLD) process, asputtering process or a chemical vapor deposition (CVD) process. Theseprocesses may be performed using an apparatus including a vacuumchamber. Thus, when the IGZO material is formed using the vacuumprocess, fabrication cost may be increased.

DISCLOSURE OF INVENTION

Some embodiments provide methods of fabricating a thin film transistorwithout use of a photolithography process and methods of fabricating anelectronic device using a sol-gel process which is capable of obtaininga thin film having a desired composition.

Some embodiments provide methods of fabricating a plurality of thin filmtransistors on a substrate having a large area.

Some embodiments provide methods of fabricating an oxide semiconductordevice having nano-structures which are less contaminated, using afabrication process of nano-structures and a sol-gel process with lowcost.

Some embodiments provide oxide semiconductor devices havingnano-structures which are less contaminated.

Some embodiments provide methods of more efficiently forming a metaloxide material of a multi-component system by introducing an oxidematerial into a porous nano-structure using a sol-gel process as a baseprocess to obtain an oxide nano-structure.

Some embodiments provide methods of forming an oxide nano-structurehaving a desired size, a desired composition and a desired phase using asol-gel process and a porous nano-structure.

In an exemplary embodiment, the method of fabricating an electronicdevice includes preparing one oxide material sol solution selected fromthe group consisting of an oxide semiconductor based sol solution, anoxide insulator based sol solution and an oxide conductor based solsolution, supplying the prepared sol solution onto a surface of a printroll to form a sol pattern, rolling the print roll along a substrate totransfer the sol pattern from the print roll onto the substrate, anddrying and heating the sol pattern transferred on the substrate to forma thin film pattern on the substrate.

The thin film pattern may be one of an oxide semiconductor layer, anoxide insulator layer and an oxide conductor layer. The sol patterntransferred on the substrate may be dried and heated at a temperature ofabout 300° C. to about 1000° C.

The method may further include applying a surface treatment process to asurface of the substrate to change the surface of the substrate into ahydrophilic surface or a hydrophobic surface before the print roll isrolled along the substrate.

Preparing the oxide material sol solution may include mixing at leastone dispersoid selected from the group consisting of a zinc compound, anindium compound, a gallium compound, a tin compound, a hafnium compound,a zirconium compound, a magnesium compound, an yttrium compound and athallium compound in a dispersion medium corresponding to the selecteddispersoid to form a disperse system, stirring the disperse system, andaging the stirred disperse system. The dispersoid may be obtained bymixing the zinc compound and a non-zinc compound in a mole ratio ofabout 1:0.1 to about 1:2. The non-zinc compound may include at least oneselected from the group consisting of the indium compound, the galliumcompound, the tin compound, the hafnium compound, the zirconiumcompound, the magnesium compound, the yttrium compound and the thalliumcompound.

The dispersion medium may include at least one selected from the groupconsisting of isopropanol, 2-methoxyethanol, dimethylformamide, ethanol,de-ionized water, methanol, acetylacetone, dimethylamineborane andacetonitrile.

The zinc compound may include at least one selected from the groupconsisting of zinc citrate dihydrate, zinc acetate, zinc acetatedihydrate, zinc acetylacetonate hydrate, zinc acrylate, zinc chloride,zinc diethyldithiocarbamate, zinc dimethyldithiocarbamate, zincfluoride, zinc fluoride hydrate, zinc hexafluoroacetylacetonatedihydrate, zinc methacrylate, zinc nitrate hexahydrate, zinc nitratehydrate, zinc trifluoromethanesulfonate, zinc undecylenate, zinctrifluoroacetate hydrate, zinc tetrafluoroborate hydrate and zincperchlorate hexahydrate.

The indium compound may include at least one selected from the groupconsisting of indium chloride, indium chloride tetrahydrate, indiumfluoride, indium fluoride trihydrate, indium hydroxide, indium nitratehydrate, indium acetate hydrate, indium acetylacetonate and indiumacetate.

The gallium compound may include at least one selected from the groupconsisting of gallium acetylacetonate, gallium chloride, galliumfluoride and gallium nitrate hydrate.

The tin compound may include at least one selected from the groupconsisting of tin acetate, tin chloride, tin chloride dihydrate, tinchloride pentahydrate and tin fluoride.

The thallium compound may include at least one selected from the groupconsisting of thallium acetate, thallium acetylacetonate, thalliumchloride, thallium chloride tetrahydrate, thallium cyclopentadienide,thallium fluoride, thallium formate, thallium hexafluoroacetylacetonate,thallium nitrate, thallium nitrate trihydrate, thallium trifluroacetateand thallium perchlorate hydrate.

The hafnium compound may include at least one selected from the groupconsisting of hafnium chloride and hafnium fluoride.

The magnesium compound may include at least one selected from the groupconsisting of magnesium acetate, magnesium chloride, magnesium nitratehydrate and magnesium sulfate.

The zirconium compound may include at least one selected from the groupconsisting of zirconium acetate, zirconium acetylacetonate, zirconiumchloride and zirconium fluoride.

The yttrium compound may include at least one selected from the groupconsisting of yttrium acetate, yttrium acetylacetonate, yttriumchloride, yttrium fluoride and yttrium nitrate.

In the disperse system, a molar concentration of the zinc compound, theindium compound, the gallium compound, the tin compound, the hafniumcompound, the zirconium compound, the magnesium compound, the yttriumcompound or the thallium compound may be about 0.1 mol/l (M) to about 10mol/l (M).

Preparing the oxide material sol solution may further include adding asol stabilizer to the disperse system. The sol stabilizer may include atleast one selected from the group consisting of mono-ethanolamine,di-ethanolamine and tri-ethanolamine.

Preparing the oxide material sol solution may further include addingacid or base to the disperse system to adjust a potential of hydrogen(pH) of the disperse system. The acid may include acetic acid (CH₃COOH),and the base may include at least one selected from the group consistingof ammonium hydroxide (NH₃OH), potassium hydroxide (KOH) and sodiumhydroxide (NaOH). The potential of hydrogen (pH) of the disperse systemmay be adjusted about 1 to 10.

The thin film pattern may have a size of about 3 mm to about 9 μm. Ashape of the thin film may be determined by a shape of the sol patternprovided on the print roll, and the thin film may have one of variousshapes, for example, a dot shape, a rectangular shape or the like.

In an exemplary embodiment, the composition used in formation of anoxide thin film includes a zinc compound, and at least one non-zinccompound selected from the group consisting of an indium compound, agallium compound, a tin compound, a hafnium compound, a zirconiumcompound, a magnesium compound, an yttrium compound and a thalliumcompound. A mole ratio of the zinc compound versus the non-zinc compoundis about 1:0.1 to about 1:2.

In an exemplary embodiment, the method of forming an oxide thin filmincludes coating a solution including at least two compounds selectedfrom the group consisting of a zinc compound, an indium compound, agallium compound, a tin compound, a hafnium compound, a zirconiumcompound, a magnesium compound, an yttrium compound and a thalliumcompound. A mole ratio of the zinc compound versus at least one of theindium compound, the gallium compound, the tin compound, the hafniumcompound, the zirconium compound, the magnesium compound, the yttriumcompound and the thallium compound is about 1:0.1 to about 1:2.

In an exemplary embodiment, the method of fabricating a liquid solutionused in formation of an oxide thin film includes mixing at least twodispersoids selected from the group consisting of a zinc compound, anindium compound, a gallium compound, a tin compound, a hafnium compound,a zirconium compound, a magnesium compound, an yttrium compound and athallium compound in a dispersion medium corresponding to the selecteddispersoids to form a disperse system. A mole ratio of the zinc compoundversus at least one of the indium compound, the gallium compound, thetin compound, the hafnium compound, the zirconium compound, themagnesium compound, the yttrium compound and the thallium compound isabout 1:0.1 to about 1:2.

In an exemplary embodiment, the method of fabricating a thin filmtransistor includes preparing an oxide semiconductor based sol solution,supplying the prepared oxide semiconductor based sol solution onto asurface of a print roll to form a sol pattern, transferring the solpattern from the surface of the print roll onto the substrate using aroll-to-roll process, and drying and heating the sol pattern transferredon the substrate to form a channel layer pattern on the substrate.

The method may further include applying a surface treatment process to asurface m of the substrate to change the surface of the substrate into ahydrophilic surface or a hydrophobic surface before the sol pattern onthe print roll is transferred onto the substrate. The sol patterntransferred on the substrate may be dried and heated at a temperature ofabout 300° C. to about 1000° C.

The method may further include sequentially forming a conductive layeracting as a gate and an insulation layer acting as a gate insulationlayer on the substrate before the sol pattern on the print roll istransferred onto the substrate.

The method may further include transferring oxide conductor based solpatterns supplied on a print roll onto the substrate using aroll-to-roll process to form a source pattern and a drain pattern afterthe channel layer pattern is formed.

The method may further include transferring an oxide conductor based solpattern supplied on a print roll onto the substrate using a roll-to-rollprocess to form a gate pattern, and transferring an oxide insulatorbased sol pattern supplied on a print roll onto the substrate using aroll-to-roll process to form a gate insulation pattern.

In an exemplary embodiment, the method of fabricating an oxidesemiconductor device includes forming an electrode on a substrate,forming a copper layer on the substrate, preparing an oxidesemiconductor based sol solution, supplying the oxide semiconductorbased sol solution onto the substrate to form a semiconductor layer of afirst conductivity type contacting the electrode on the substrate, andsupplying acid onto the copper layer and applying a thermal treatment tothe copper layer to form a copper oxide nano-structure of a secondconductivity type that is grown from the copper layer to contact theelectrode.

Prior to formation of the electrode, the method may further includeforming a gate electrode layer on the substrate, and forming a gateinsulation layer on the gate electrode layer. Forming the electrode mayinclude forming first, second and third source/drain electrodes on thegate insulation layer. The first source/drain electrode may be formedbetween the second and third source/drain electrodes. Forming thesemiconductor layer of the first conductivity type may include providingan oxide semiconductor based sol solution on the gate insulation layerbetween the first and second source/drain electrodes to form an oxidesemiconductor layer of a first conductivity type contacting both thefirst and second source/drain electrodes. The copper layer may be formedon a top surface of the third source/drain electrode and the copperoxide nano-structure may be grown from the copper layer to contact thecontact the first source/drain electrode.

The thermal treatment applied to the copper layer may be performed at atemperature of about 300° C. to about 1000° C. The thermal treatment maybe performed in vacuum. The thermal treatment may be performed using atleast one of a nitrogen gas, a hydrogen gas and an oxygen gas as anambient gas.

Preparing the oxide semiconductor based sol solution may include mixingat least one dispersoid selected from the group consisting of a zinccompound, an indium compound, a gallium compound, a tin compound, ahafnium compound, a zirconium compound, a magnesium compound, an yttriumcompound and a thallium compound in a dispersion medium corresponding tothe selected dispersoid to form a disperse system, stirring the dispersesystem, and aging the stirred disperse system.

The dispersoid may be formed by mixing the zinc compound and at leastone non-zinc compound selected from the group consisting of the indiumcompound, the gallium compound, the tin compound, the hafnium compound,the zirconium compound, the magnesium compound, the yttrium compound andthe thallium compound in a mole ratio of about 1:0.1 to about 1:2,respectively. The dispersion medium may include at least one selectedfrom the group consisting of isopropanol, 2-methoxyethanol,dimethylformamide, ethanol, de-ionized water, methanol, acetylacetone,dimethylamineborane and acetonitrile.

In the disperse system, a molar concentration of the zinc compound, theindium compound, the gallium compound, the tin compound, the hafniumcompound, the zirconium compound, the magnesium compound, the yttriumcompound or the thallium compound may be about 0.1 mol/l (M) to about 10mol/l (M).

Preparing the oxide material sol solution may further include addingacid or base to the disperse system to adjust a potential of hydrogen(pH) of the disperse system. The acid may include acetic acid (CH₃COOH),and the base may include at least one selected from the group consistingof ammonium hydroxide (NH₃OH), potassium hydroxide (KOH) and sodiumhydroxide (NaOH). The potential of hydrogen (pH) of the disperse systemmay be adjusted within the range of about 1 to 10. In particular, thepotential of hydrogen (pH) of the disperse system may be adjusted about3.8 to 4.2.

In an exemplary embodiment, the oxide semiconductor device includes agate electrode layer formed on a substrate, a gate insulation layerformed on the gate electrode layer, second and third source/drainelectrodes formed on the gate insulation layer, a first source/drainelectrode disposed between the second and third source/drain electrodes,a semiconductor layer of a first conductivity type formed on the gateinsulation layer between the first and second source/drain electrodes toact as a channel region that connects the first source/drain electrodeto the second source/drain electrode, a copper layer formed on the thirdsource/drain electrode, and a copper oxide nano-structure of a secondconductivity type grown from the copper layer to contact the firstsource/drain electrode.

The oxide semiconductor device may be a complementarymetal-oxide-semiconductor (CMOS) device.

In an exemplary embodiment, the semiconductor device includes a copperoxide nano-structure of a first conductivity type, and an oxidesemiconductor layer of a second conductivity type surrounding an outercircumference of the copper oxide nano-structure to form a PN junctiontogether with the copper oxide nano-structure.

The oxide semiconductor device is a junction field effect transistor(JFET). In this case, the oxide semiconductor device may further includea pair of source/drain electrodes formed at both ends of the copperoxide nano-structure respectively, and a gate electrode formed on theoxide semiconductor layer opposite to the copper oxide nano-structure.

In an exemplary embodiment, the method of fabricating an oxidenano-structure using a sol-gel process and a porous nano-structure isprovided. The method includes steps of (a) applying a surface treatmentto a substrate having the porous nano-structure, (b) injecting an oxidecompound sol material into the porous nano-structure, (c) drying andheating the oxide compound sol material using a thermal treatment totransform the oxide compound sol material in the porous nano-structureinto an oxide nano-structure through a gelled pattern, and (d)separating the porous nano-structure from the oxide nano-structure.

The substrate having the porous nano-structure may be formed of ananodic aluminum oxide (AAO) material or an acrylamide (AAM) material.

In the step (b), the oxide compound sol material may be injected intothe porous nano-structure using a spin coating process or a dip coatingprocess.

In the step (b), the oxide compound sol material may be injected intothe porous nano-structures at a temperature of about 80° C. to about100° C. under a vacuum condition of about 1×10⁻¹ torr to about 1×10⁻⁷torr.

In the step (b), the oxide compound sol material may be formed by mixingat least two dispersoids selected from the group consisting of a zinccompound, an indium compound, a gallium compound, a tin compound, ahafnium compound, a zirconium compound, a magnesium compound, an yttriumcompound and a thallium compound in a dispersion medium corresponding tothe selected dispersoids to form a disperse system, stirring thedisperse system, and aging the stirred disperse system. A mole ratio ofthe zinc compound versus at least one selected from the group consistingof the indium compound, the gallium compound, the tin compound and thethallium compound may be about 1:0.1 to about 1:2.

The dispersion medium may include at least one selected from the groupconsisting of isopropanol, 2-methoxyethanol, dimethylformamide, ethanol,de-ionized water, methanol, acetylacetone, dimethylamineborane andacetonitrile.

The zinc compound may include at least one selected from the groupconsisting of zinc citrate dihydrate, zinc acetate, zinc acetatedihydrate, zinc acetylacetonate hydrate, zinc acrylate, zinc chloride,zinc diethyldithiocarbamate, zinc dimethyldithiocarbamate, zincfluoride, zinc fluoride hydrate, zinc hexafluoroacetylacetonatedihydrate, zinc methacrylate, zinc nitrate hexahydrate, zinc nitratehydrate, zinc trifluoromethanesulfonate, zinc undecylenate, zinctrifluoroacetate hydrate, zinc tetrafluoroborate hydrate and zincperchlorate hexahydrate.

The indium compound may include at least one selected from the groupconsisting of indium chloride, indium chloride tetrahydrate, indiumfluoride, indium fluoride trihydrate, indium hydroxide, indium nitratehydrate, indium acetate hydrate, indium acetylacetonate and indiumacetate.

The gallium compound may include at least one selected from the groupconsisting of gallium acetylacetonate, gallium chloride, galliumfluoride and gallium nitrate hydrate.

The tin compound may include at least one selected from the groupconsisting of tin acetate, tin chloride, tin chloride dihydrate, tinchloride pentahydrate and tin fluoride.

The thallium compound may include at least one selected from the groupconsisting of thallium acetate, thallium acetylacetonate, thalliumchloride, thallium chloride tetrahydrate, thallium cyclopentadienide,thallium fluoride, thallium formate, thallium hexafluoroacetylacetonate,thallium nitrate, thallium nitrate trihydrate, thallium trifluroacetateand thallium perchlorate hydrate.

A molar concentration of the zinc compound, the indium compound, thegallium compound, the tin compound or the thallium compound in thedisperse system may be about 0.1 mol/l (M) to about 10 mol/l (M).

Preparing the oxide material sol solution may further include adding asol stabilizer to the disperse system. The sol stabilizer may have thesame moles as the zinc compound in the disperse system.

The sol stabilizer may include at least one selected from the groupconsisting of mono-ethanolamine, di-ethanolamine and tri-ethanolamine.

Preparing the oxide material sol solution may further include addingacid or base to the disperse system to adjust a potential of hydrogen(pH) of the disperse system.

The potential of hydrogen (pH) of the disperse system may be lowered ifacetic acid (CH₃COOH) is added to the disperse system. Alternatively,the potential of hydrogen (pH) of the disperse system may be heightenedif a base (e.g., ammonium hydroxide, potassium hydroxide or sodiumhydroxide) is added to the disperse system. Thus, the potential ofhydrogen (pH) of the disperse system may be appropriately adjustedwithin the range of about 1 to 10 by adding the acid or the base to thedisperse system.

The potential of hydrogen (pH) of the disperse system may be adjustedwithin the range of about 3.8 to 4.2.

In the step (c), the thermal treatment may be performed at a temperatureof about 300° C. to about 1000° C.

In the step (d), separating the porous nano-structure from the oxidenano-structure may include etching the porous nano-structures using asodium hydroxide solution and obtaining the oxide nano-structure using acentrifugal separation process.

In the step (d), a shape of the oxide nano-structure may be determinedby a shape of the porous nano-structure. The oxide nano-structure may beformed to have a dot shape or a cylindrical shape. The oxidenano-structure may be formed to have a size of about several nanometersto about several micrometers.

SUMMARY

According to the methods of forming an electronic device such as a thinfilm transistor using sol-gel processes and roll-to-roll processesaccording to the exemplary embodiments, the electronic device such asthe thin film transistor including a desired material of amulti-component system may be easily formed by selecting an appropriatesol solution and changing composition of the sol solution. Further,according to the exemplary embodiments, thin film patterns may be easilyformed on a substrate having a large area with high throughput and lowcost. In addition, since the fabrication methods according to theexemplary embodiments utilize roll-to-roll processes with print rolls, ahigh process throughput may be provided and mass production may beavailable. Moreover, various and diverse electronic devices other thanthe thin film transistors may also be formed with high throughput bychanging an order of the roll-to-roll processes and/or shapes and sizesof patterns. Furthermore, the exemplary embodiments may suppress acoffee ring effect to enhance the thickness uniformity of the thin filmpatterns.

According to the methods of forming an electronic device such as a thinfilm transistor using sol-gel processes and roll-to-roll processesaccording to the exemplary embodiments, self-aligned copper oxidenano-structures may be obtained through the sol-gel processes andsubsequent thermal treatment processes. Thus, the nano-structures may bedisposed at desired locations of the electronic device even without useof complicated processes such as separation, refinement and arrangement.That is, even photolithography processes may not be required. Further,according to the exemplary embodiments, catalyst components may notremain at ends of the nano-structures. Thus, single crystalline purenano-structures can be obtained. Moreover, oxide semiconductor materialsof a multi-component system can be more efficiently formed as comparedwith the conventional art, and diverse oxide semiconductor materials canbe formed by changing and/or adjusting the properties of the solmaterial. Furthermore, it may be easy to change a phase of the thinfilm, a size of the nano-structures or electrical characteristics of thenano-structures by varying temperature of a thermal treatment and/orprocess time of the thermal treatment.

According to the methods of forming an electronic device such as a thinfilm transistor using sol-gel processes and roll-to-roll processesaccording to the exemplary embodiments, oxide nano-structures can beobtained by injecting an oxide material into porous nano-structuresusing a sol-gel process as a basic process. Thus, a metal oxide materialof a multi-component system can be more effectively formed as comparedwith the conventional art, and the oxide nano-structures can be formedto have a desired phase, a desired composition and/or a desired size.

Further, unlike the fabrication methods of nano-structures usingconventional deposition processes, the oxide material can be easilyinjected into the porous nano-structures using a sol-gel process. Thus,the exemplary embodiments can provide the possibility of massproduction. In addition, the size of the nano-structure can be easilycontrolled by adjusting the size of the porous nano-structure in whichan oxide material solution (e.g., liquid oxide compound sol) isinjected, and it may also be easy to change a type and a composition ofthe sol solution. Moreover, a phase of the oxide material can be easilychanged by changing process conditions of thermal treatment.

In addition, self-aligned oxide nano-structures can be formed using awell-aligned porous anodic aluminum oxide (AAO) solution and anIn—Ga—ZnO (IGZO) solution. Thus, the exemplary embodiments may providethe possibility of mass production. Further, unlike the conventionaldeposition process utilizing the vacuum apparatus and high temperatureprocess, the exemplary embodiments may not require gas, powder andcatalyst. Thus, low cost devices can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating a substrate prior to aroll-to-roll process according to an exemplary embodiment.

FIG. 2 is a perspective view illustrating a method of printing andtransferring sol solution patterns from a print roll surface onto asubstrate using a roll-to-roll process according to an exemplaryembodiment.

FIG. 3 is a perspective view illustrating a method of printing andtransferring sol solution patterns from a print roll surface onto asubstrate using a roll-to-roll process according to another exemplaryembodiment.

FIG. 4 is a perspective view illustrating a method of printing andtransferring sol solution patterns from a print roll surface onto asubstrate using a roll-to-roll process according to yet anotherexemplary embodiment.

FIGS. 5 and 6 are perspective views illustrating methods of fabricatinga thin film transistor using roll-to-roll processes according to someexemplary embodiments.

FIG. 7 is a cross sectional view illustrating a thin film transistorfabricated according to an exemplary embodiment.

FIG. 8 is a cross sectional view illustrating a thin film transistorfabricated according to another exemplary embodiment.

FIGS. 9 to 12 are perspective views illustrating a method of fabricatingan oxide semiconductor device according to an exemplary embodiment.

FIG. 13 is a perspective view illustrating an oxide semiconductor deviceaccording to another exemplary embodiment.

FIGS. 14A and 14B are cross sectional views illustrating an oxidesemiconductor device according to yet another exemplary embodiment.

FIG. 15 is a scanning electron microscope (SEM) picture illustratingP-type copper oxide nano-wires that can be applied to an oxidesemiconductor device fabricated according to an exemplary embodiment.

FIGS. 16 to 19 are schematic drawings illustrating a method of formingoxide nano-structures using a porous nano-structure and a sol-gelprocess according to an exemplary embodiment.

FIG. 20 is a merged drawing including a TG-DSC measurement graph of IGZOsolution and transmission electron microscope (TEM) pictures of phasesof IGZO materials cured at various temperatures.

DETAILED DESCRIPTION

Exemplary embodiments of the inventive concept will be described morefully hereinafter with reference to the accompanying drawings. Theexemplary embodiments may, however, be embodied in many different formsand should not be construed as limited to the embodiments set forthherein. In the drawings, the sizes and the shapes of elements (e.g.,layers and regions) are exaggerated for clarity.

<Electronic Devices and Methods of Fabricating the Same Using a Sol-GelProcess and a Roll-To-Roll Process>

Fabrication of semiconductor devices and display devices may correspondto typical devices industry. The semiconductor devices and the displaydevices may be manufactured in a vacuum chamber having a relativelylarge size using semiconductor fabrication processes. For example, thinfilm transistors may be formed using a chemical vapor deposition (CVD)process, a pulsed laser deposition (PLD) process and/or a sputteringprocess that utilizes a vacuum apparatus including a vacuum chamber.Vacuum processes using the vacuum chamber may provide advantages thatproduce high quality thin films since the thin films are formed invacuum. However, the vacuum process may have a disadvantage of longdeposition time. This is because it takes long time to evacuate thevacuum chamber. Further, the vacuum process may need a high pricedapparatus and may need a photolithography process for forming patternshaving desired shapes.

Unlike the deposition process utilizing the conventional vacuum process,the deposition process utilizing a sol-gel process may need a low pricedapparatus and may provide a large area of deposition. Thus, the sol-gelprocess may have an advantage of a high throughput. As a result, thesol-gel process may be suitable for mass production. For the reasonsdescribe above, methods of fabricating an electronic device using thesol-gel process have been proposed. For example, a sol solution may becoated on a substrate using a spin coating method, a dip coating method,an ink-jet coating method or a nano imprint method in order to fabricateelectronic devices.

In general, materials used in fabrication of the electronic devices withthe sol-gel process may include an organic semiconductor material suchas pentacene and an inorganic semiconductor material such as a zincoxide (ZnO) material. The organic semiconductor material may be morereadily damaged by oxygen and water. Thus, the organic semiconductormaterials have been faced with some technical limitations in improvingthe characteristics of organic semiconductor based thin film transistorsformed using the sol-gel process as compared with amorphous silicon thinfilm transistors (a-Si TFTs). Meanwhile, oxide semiconductor based TFTsmay exhibit excellent electrical characteristics including carriermobility as compared with the a-Si TFTs. The oxide material based thinfilms may have excellent electrical characteristics as compared with theorganic material based thin films. Further, the oxide material basedthin films may stably maintain their characteristics even though theyare exposed to oxygen or water.

The spin coating method is one of the most popular deposition techniquesused in fabrication of the electronic devices using the sol-gel process.The spin coating method may include loading a substrate on a chuck of aspin coater, supplying a sol solution onto the substrate, and rotatingthe substrate with the chuck to form a uniform and thin film coated onthe substrate. When the sol solution is an oxide material sol solution,the thin film coated on the substrate may be used as an active channellayer of the thin film transistors (TFTs). The spin coating method mayproduce a desired composition material with the sol-gel process and mayreduce the process time for fabricating the TFTs as compared with thepulsed laser deposition (PLD) process and the sputtering process.However, according to the spin coating method, the thin film may becoated on an entire surface of the substrate like the thin film formedusing the vacuum process. Thus, in the event that the spin coatingmethod is used in formation of the thin film, an additional process forpatterning the thin film may be required to form material patternshaving desired shapes.

Another method of forming a thin film using the sol-gel process may be adip coating method that includes dipping a substrate into a solsolution. The dip coating method may produce a desired thin film on thesubstrate within a relatively shorter process time as compared with thespin coating method. However, the thin film formed using the dip coatingmethod may have a less uniform thickness than the thin film formed usingthe spin coating method. Thus, the dip coating method may not besuitable for fabrication of the TFTs or the electronic devices thatrequire a uniform thin film.

Yet another method of forming a thin film with the sol-gel process maybe an ink-jet coating method. According to the ink-jet coating method, athin film transistor (TFT) may be formed by injecting an oxide materialsol solution into an ink-jet apparatus, supplying the oxide material solsolution onto predetermined regions (active channel regions) of asubstrate, and curing the oxide material sol solution on the substrate.This ink-jet coating method may have an advantage that the sol solutioncan be selectively supplied onto the predetermined regions of thesubstrate. However, according to the ink-jet coating method, a thin filmformed on the substrate may have a non uniform thickness due to a coffeering effect. Further, the ink-jet coating method may cause a pooradhesion between the thin film and an underlying layer (or overlyinglayer). The coffee ring effect means that the thin film has a nonuniform thickness after the curing step. That is, the thickness of thethin film on a central region may be different from the thickness of thethin film on an edge region

Still yet another method of forming a thin film with the sol-gel processmay be a nano imprint method. The nano imprint method may produce smalland fine thin film patterns having a space or a width which is less thana resolution limit of the photolithography process. The nano imprintmethod may include various methods. For example, the nano imprint methodmay be performed by coating a sol-gel material on a substrate andpatterning the sol-gel material using a nano imprint technique.Alternatively, the nano imprint method may be performed by bringing astamp into contact with a substrate and forming desired patterns using adip coating method. Alternatively, the nano imprint method may beperformed by coating a stamp with a sol solution and pressing the stamponto a substrate. However, the nano imprint method may cause damage andcontamination of substrate. Further, when the stamp has a large area, itmay be difficult to press the stamp with uniform pressure. That is, itmay be difficult to uniformly form all the thin film patterns on thesubstrate having a large area.

Accordingly, the exemplary embodiments may provide methods offabricating an electronic device such as a thin film transistor, whichare capable of reducing process time and producing uniform thin filmpatterns even without use a photolithography process.

Further, the exemplary embodiments may provide methods of fabricating anelectronic device using a sol-gel process which is capable of obtaininga thin film having a desired composition.

Exemplary embodiments of the inventive concept will be described morefully hereinafter with reference to the accompanying drawings. Theexemplary embodiments may, however, be embodied in many different formsand should not be construed as limited to the embodiments set forthherein. In the drawings, the sizes and the shapes of elements (e.g.,layers and regions) are exaggerated for clarity. Like designators in thedrawings and description refer to like elements throughout thisdescription.

FIG. 1 is a perspective view illustrating a substrate prior to aroll-to-roll process according to an exemplary embodiment. Referring toFIG. 1, a surface of a substrate 101, particularly, predeterminedsurface regions of the substrate 101 may be exposed to a surfacetreatment process, thereby changing into hydrophilic surfaces orhydrophobic surfaces. For example, the surface treatment process forobtaining the hydrophilic surfaces may be performed using sodiumhydroxide (NaOH) with oxygen plasma, piranha solution, or mixture ofde-ionized water and acetone, and the surface treatment process forobtaining the hydrophobic surfaces may be performed usingpolydimethylsiloxane (PDMS), toluene, oroctadecyltetrachlorosilane-self-assembled-monolayers (OTS-SAMs). Thesurface treatment process may improve a thickness uniformity of a thinfilm when a print roll is stamped on a substrate using a subsequentroll-to-roll process to transfer sol patterns from the print roll ontothe substrate. The surface treatment process may be applied to an entiresurface of the substrate or the predetermined surface regions (e.g.,device regions) of the substrate.

FIGS. 2 to 4 are schematic perspective views illustrating processes forforming thin film patterns having a property of semiconductors,insulators or conductors according to a characteristic of oxide solusing a sol-gel process and a roll-to-roll process. Referring to FIGS. 2to 4, a sol solution having a property of an oxide semiconductor, anoxide conductor, or an oxide insulator may be prepared before thin filmpatterns for electronic devices are printed on the substrate 101 by aroll-to-roll process utilizing a print roll 105, 106 or 107.

Forming the sol solution used in the roll-to-roll process may includemixing compound dispersoid having a property of a desired material(e.g., a semiconductor, a conductor or an insulator) in a dispersionmedium corresponding to the selected dispersoid to form a dispersesystem, stirring the disperse system, and aging the stirred dispersesystem. The compound dispersoid may include at least one selected fromthe group consisting of a zinc compound, an indium compound, a galliumcompound, a tin compound, a hafnium compound, a zirconium compound, amagnesium compound, an yttrium compound and a thallium compound. Inparticular, the dispersoid of the sol solution may include a zinccompound. For example, the dispersoid of the sol solution may be formedby mixing the zinc compound and a non-zinc compound (e.g., at least oneof indium compound, gallium compound, tin compound, hafnium compound,zirconium compound, magnesium compound, yttrium compound and thalliumcompound) in a mole ratio of about 1:0.1 to about 1:2. Further, a molarconcentration of the zinc compound, the indium compound, the galliumcompound, the tin compound, the hafnium compound, the zirconiumcompound, the magnesium compound, the yttrium compound or the thalliumcompound in the disperse system may be about 0.1 mol/l (M) to about 10mol/l (M).

The dispersion medium of the sol solution may include at least oneselected from the group consisting of isopropanol, 2-methoxyethanol,dimethylformamide, ethanol, de-ionized water, methanol, acetylacetone,dimethylamineborane and acetonitrile.

Specifically, the zinc compound used as the dispersoid of the solsolution may include at least one selected from the group consisting ofzinc citrate dihydrate, zinc acetate, zinc acetate dihydrate, zincacetylacetonate hydrate, zinc acrylate, zinc chloride, zincdiethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc fluoride,zinc fluoride hydrate, zinc hexafluoroacetylacetonate dihydrate, zincmethacrylate, zinc nitrate hexahydrate, zinc nitrate hydrate, zinctrifluoromethanesulfonate, zinc undecylenate, zinc trifluoroacetatehydrate, zinc tetrafluoroborate hydrate and zinc perchloratehexahydrate.

Further, the indium compound used as the dispersoid of the sol solutionmay include at least one selected from the group consisting of indiumchloride, indium chloride tetrahydrate, indium fluoride, indium fluoridetrihydrate, indium hydroxide, indium nitrate hydrate, indium acetatehydrate, indium acetylacetonate and indium acetate.

The gallium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of galliumacetylacetonate, gallium chloride, gallium fluoride and gallium nitratehydrate.

The tin compound used as the dispersoid of the sol solution may includeat least one selected from the group consisting of tin acetate, tinchloride, tin chloride dihydrate, tin chloride pentahydrate and tinfluoride.

The thallium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of thalliumacetate, thallium acetylacetonate, thallium chloride, thallium chloridetetrahydrate, thallium cyclopentadienide, thallium fluoride, thalliumformate, thallium hexafluoroacetylacetonate, thallium nitrate, thalliumnitrate trihydrate, thallium trifluroacetate and thallium perchloratehydrate.

The hafnium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of hafniumchloride and hafnium fluoride.

The magnesium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of magnesiumacetate, magnesium chloride, magnesium nitrate hydrate and magnesiumsulfate.

The zirconium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of zirconiumacetate, zirconium acetylacetonate, zirconium chloride and zirconiumfluoride.

The yttrium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of yttriumacetate, yttrium acetylacetonate, yttrium chloride, yttrium fluoride andyttrium nitrate.

When the sol solution is formed, a sol stabilizer may be added to thedisperse system. The sol stabilizer may include mono-ethanolamine,di-ethanolamine or tri-ethanolamine. The sol stabilizer may have thesame moles as the compound material of the dispersoid in the dispersesystem.

Moreover, when the sol solution is formed, acid or base may be added tothe disperse system to adjust a potential of hydrogen (pH) of thedisperse system. For example, the potential of hydrogen (pH) of thedisperse system may be lowered if acetic acid (CH₃COOH) is added to thedisperse system, and the potential of hydrogen (pH) of the dispersesystem may be heightened if a base (e.g., ammonium hydroxide, potassiumhydroxide or sodium hydroxide) is added to the disperse system. Thus,the potential of hydrogen (pH) of the disperse system may beappropriately adjusted within the range of about 1 to 10 by adding theacid (e.g., acetic acid) or the base to the disperse system.

The oxide semiconductor based sol solution (e.g., zinc oxide based solsolution) prepared by the above methods may be provided on a surface ofthe print roll 105, 106 or 107 in a pattern form. Referring to FIG. 2,the sol solution may be provided on the surface of the cylindrical printroll 105 in a plurality of patterns 105 a. For example, the sol solutionmay be selectively coated on block patterns (for stamping) formed on thesurface of the print roll 105, thereby providing the plurality of solpatterns 105 a on the print roll 105. The print roll 105 having the solpatterns 105 a may be then rolled and stamped on the substrate 101,thereby transferring the sol patterns 105 a onto the substrate 101. As aresult, oxide semiconductor based sol patterns 102 may be formed on thesubstrate 101.

After forming the oxide semiconductor based sol patterns 102 on thesubstrate 101, the sol patterns 102 may be dried and heated using athermal treatment process to transform the sol patterns 102 into gelledpatterns. As a result, oxide semiconductor thin film patterns may beformed on the substrate 101, and the oxide semiconductor thin filmpatterns may be used as active channel layers of desired electronicdevices (e.g., thin film transistors or diodes). The thermal treatmentprocess for forming the gelled patterns or the thin film patterns may beperformed at a temperature of about 300° C. to about 1000° C.

According to the above exemplary embodiment, thin film patterns may beeasily obtained even on a substrate having a large area through astamping print technique that is employed in a sol-gel process and aroll-to-roll process. That is, the present embodiment may improvethroughput of the thin film patterns having a uniform thickness evenwithout use of a vacuum apparatus. That is, the present embodiment mayresolve the disadvantages of the ink-jet printing method even withoutuse of a vacuum process. Further, the plurality of thin film patternsmay be printed on the substrate 101 by rolling the print roll 105. Thus,the substrate 101 may be less damaged and more uniformly pressurized ascompared with the conventional nano imprint method.

The methods proposed by the inventor(s) may be applied to not onlyformation of the oxide semiconductor thin film patterns described withreference to FIG. 2 but also formation of oxide insulator thin filmpatterns or oxide conductor thin film patterns by changing compositionof the sol solution.

Referring to FIG. 3, an oxide insulator based sol solution (e.g., ahafnium compound material based sol solution, a zirconium compoundmaterial based sol solution, or a dispersoid based sol solutioncontaining a large quantity of hafnium compound and/or zirconiumcompound) may be provided on the surface of the cylindrical print roll106, thereby forming sol patterns 106 a on the cylindrical print roll106, and the sol patterns 106 a on the cylindrical print roll 106 may betransferred on the substrate 101 by rolling the cylindrical print roll106, thereby forming sol patterns 103 on the substrate 101. The solpatterns 103 may be dried and heated using the same manners as thethermal treatment process described with reference to FIG. 2 to formoxide insulator thin film patterns on the substrate 101. The oxideinsulator thin film patterns may be used as components of desiredelectronic devices, for example, thin film transistors or diodes.

FIG. 4 is a perspective view illustrating a method of forming oxideconductor thin film patterns on a substrate using the sol-gel processand the roll-to-roll process described above. Referring to FIG. 4, anoxide conductor based sol solution may be provided on the surface of thecylindrical print roll 107, thereby forming sol patterns 107 a on thecylindrical print roll 107, and the sol patterns 107 a on thecylindrical print roll 107 may be transferred on the substrate 101 byrolling the cylindrical print roll 107, thereby forming sol patterns 104on the substrate 101. The sol patterns 104 may be dried and heated usingthe same manners as the thermal treatment process described withreference to FIG. 2 to form oxide conductor thin film patterns on thesubstrate 101. The oxide conductor thin film patterns may be used ascomponents of desired electronic devices, for example, thin filmtransistors or diodes.

The processes described with reference to FIGS. 2, 3 and 4 may becombined with each other to form a desired electronic device. Forexample, the desired electronic device may be formed by appropriatelyadjusting an order of the processes illustrated in FIGS. 2 to 4 and bychanging the shape of the patterns. The shapes of the patterns formed onthe substrate 101 may depend on the shapes of the sol patterns providedon the surface of the print roll 105, 106 or 107 and may have diverseand various forms, for example, dot shapes, rectangular shapes or thelike. The sizes of the thin film patterns may be within the range ofseveral nanometers (mm) to several micrometers (μm), particularly, ofabout 3 mm to about 9 μm.

FIGS. 5 and 6 are perspective views illustrating methods of fabricatinga thin film transistor (TFT) using a sol-gel process and a roll-to-rollprocess according to some exemplary embodiments. In the presentexemplary embodiment, the roll-to-roll process may be applied toformation of semiconductor channel layers and source/drain layers of theTFT.

As illustrated in FIG. 5, conductive layer 201 and an insulation layer202 may be sequentially formed on a substrate 101. The conductive layer201 may act as a gate and the insulation layer 202 may act as a gateinsulation layer. Subsequently, a sodium hydroxide plasma treatment oran oxygen plasma treatment may be applied to the insulation layer 202 toprovide a preparation for a subsequent roll-to-roll process (ahydrophilic surface treatment or a hydrophobic surface treatment). Usingthe same manners as described with reference to FIG. 2, an oxidesemiconductor based sol solution may be then provided on a surface ofthe print roll 205 to form sol patterns 205 a on the print roll 205. Aroll-to-roll process may be performed using the print roll 205 havingthe sol patterns 205 a, thereby forming sol patterns 203 transferred onthe insulation layer 202 which is formed on the substrate 101. The solpatterns 203 may be dried and heated using the same manners as thethermal treatment process described with reference to FIG. 2. As aresult, oxide semiconductor channel layer patterns 203′ may be formed onthe insulation layer 202, as illustrated in FIG. 6.

Subsequently, an oxide conductor based sol solution may be provide on asurface of another pint roll 206 to form sol patterns 206 a on the printroll 206. Another roll-to-roll process may be performed using the printroll 206 having the sol patterns 206 a, thereby forming source/drainpatterns 211 and 212 on the oxide semiconductor channel layer patterns203′. The source/drain patterns 211 and 212 may also be dried and heatedusing the same manners as the thermal treatment process described withreference to FIG. 2. Thus, a pair of source/drain patterns 211′ and 212′may be formed on both ends of each of the channel layer patterns 203′,as illustrated in FIG. 7. As a result, a plurality of thin filmtransistors illustrated in FIG. 7 may be easily formed in largequantities.

In the above exemplary embodiments, the sol-gel process and theroll-to-roll process may be used only in formation of the semiconductorchannel layers and the source/drain patterns. However, the sol-gelprocess and the roll-to-roll process may be used even in formation ofother components than the semiconductor channel layers and thesource/drain patterns. For example, the sol-gel process and theroll-to-roll process may also be used in formation of gates patterns(e.g., gate electrodes) and gate insulation layers constituting the thinfilm transistors. That is, the gate patterns may be formed bytransferring oxide conductor based sol patterns provided on a surface ofa print roll onto a substrate with the above described roll-to-rollprocess (refer to FIG. 4), and the gate insulation layers may be formedby transferring oxide insulator based sol patterns provided on a surfaceof a print roll onto a substrate with the above described roll-to-rollprocess (refer to FIG. 3). After the roll-to-roll process is performed,a thermal treatment process for transforming the sol patterns intogelled patterns may be required to form the thin film patterns.

According to the above exemplary embodiment, inverted staggered type ofthin film transistors having a common bottom gate 201 may be formed.That is, the gate 201 may be formed to be adjacent to the substrate 101,and the source/drain patterns 211′ and 212′ may be formed on the channellayer opposite to gate 201. However, the inventive concept is notlimited to the above exemplary embodiment s. That is, staggered type ofthin film transistors having top gates 301 disposed on the channellayers opposite to the substrate may also be formed by appropriatelychanging an order of the roll-to-roll processes and sizes of thepatterns, as illustrated in FIG. 8. In this case, source/drain patterns311 and 312 may be formed on a substrate 101 using a sol-gel process anda roll-to-roll process, and channel layers 303, gate insulation layers302 and gates 301 may be sequentially formed on the substrate includingthe source/drain patterns 311 and 312.

The inventive concept is not limited to the above exemplary embodimentsand the accompanying drawings. The scope of the inventive concept is tobe determined by the following claims, and it will be apparent to thoseskilled in the art that various changes and modifications may be madewithout departing from the spirit and scope of the inventive concept.

<Oxide Semiconductors and Methods of Fabricating the Same Using aSol-Gel Process and Nano-Structures>

Nano-devices may be formed by applying nano-structures fabricated usingvarious manners to electronic devices such as semiconductor devices.Recently, a study on the nano-devices has been increasingly demandedbecause the nano-devices have advantages of fast operation speed withlarge data.

In general, the nano-structures may be fabricated using avapor-liquid-solid (VLS) mechanism, a solution-liquid-solid (SLS)mechanism, or other mechanisms by chemical reactions or thermaltreatments. A metal catalyst may be required to fabricate thenano-structure using the VLS mechanism, and the metal catalyst mayinclude metal (e.g., gold (Au), nickel (Ni) or iron (Fe)), which iscapable of lowering a melting point of a material. When the VLSmechanism is used in fabrication of the nano-structures, the locationand the diameter of the nano-structures may be controlled by thelocation and size of the catalysts. For example, in the event that achemical vapor deposition (CVD) process is used to form thenano-structures, gaseous reactants may be combined with gold (on goldnano-cloud surfaces) acting as catalysts to generate nuclei and thenuclei may grow to form silicon nano-structures having a multi shell.

In order to fabricate nan-structures using an SLS mechanism, a liquidprecursor and a catalyst such as gold may be required. The gold actingas the catalyst may increase overall yield of the nano-structures or maycontrol the diameter and the location of the nano-structures. Forexample, when silicon nano-wires are fabricated, gold nano-particles,(C₆H₅)₂SiH₂ and hexane may be used as a metal catalyst, a silicon liquidprecursor and a solvent, respectively. In this case, the (C₆H₅)₂SiH₂ maybe decomposed into silicon atoms and the silicon atoms may be alloyedwith the gold nano-particles to extract silicon. As a result, siliconnano-structures may be formed. The metal catalyst may control thediameter of the nano-structures and may control the location of thenano-structures. The nano-structures fabricated using the SLS mechanismmay be grown at a relatively low temperature as compared with thenano-structures fabricated using the VLS mechanism. However, thecrystallinity of the nano-structures fabricated using the SLS mechanismmay be degraded as compared with the crystallinity of thenano-structures fabricated using the VLS mechanism.

The methods of fabricating the nano-structures using the aforementionedVLS mechanism use a deposition process that requires a high pricedvacuum apparatus and a catalyst. Thus, the fabrication process may becomplicated and the fabrication cost may be increased. Further, in theevent that the nano-structures are fabricated using the SLS mechanism,the crystallinity of the nano-structures may be degraded and thefabrication process may be complicated. Moreover, it may be difficult todirectly apply the nano-structures obtained using the VLS mechanism orthe SLS mechanism to the semiconductor devices. That is, complicatedprocesses, for example, separation, refinement and arrangement may berequired after growth of the nano-structures in order to apply thenano-structures obtained using the VLS mechanism or the SLS mechanism tothe semiconductor devices. In addition, catalyst components may remainat ends of the fabricated nano-structures, for example, nano-wires.Thus, it may be difficult to obtain single crystalline purenano-structures without contamination.

Accordingly, the exemplary embodiments may provide methods offabricating oxide semiconductor device having nano-structures with lesscontamination using a simplified and low cost fabrication process and asol-gel process.

FIGS. 9 to 12 are perspective views illustrating a method of fabricatingan oxide semiconductor device according to an exemplary embodiment. Thepresent exemplary embodiment will be described in conjunction with afabrication process of a complementary metal-oxide-semiconductor (CMOS)device such as a CMOS transistor. However, the inventive concept is notlimited to the fabrication process of the CMOS device. For example, theinventive concept may be applied to fabrication processes ofmetal-oxide-semiconductor field effect transistors (MOSFETs), junctionfield effect transistors (JFETs), PN diodes or the like.

Referring to FIG. 9, a gate electrode 1030 and a gate insulation layer1050 may be formed on a substrate 1010 (e.g., a plastic based flexiblesubstrate, a glass substrate or a silicon substrate). The gate electrode1030 may be formed of a metal layer, and the gate insulation layer 1050may be formed of a silicon oxide layer. A first source/drain electrode1100, a second source/drain electrode 1200 and a third source/drainelectrode 1300 may be formed on the gate insulation layer 1050. Thefirst source/drain electrode 1100 may be formed between the second andthird source/drain electrodes 1200 and 1300. As used herein the term“source/drain electrode” is intended to indicate any one of a sourceelectrode and a drain electrode. These source/drain electrodes 1100,1200 and 1300 may be formed of a metal material. The gate insulationlayer 1050 may be formed by depositing an insulation material using asputtering process or a plasma enhanced chemical vapor deposition(PECVD) process.

Referring to FIG. 10, a copper layer 1400 may be formed on the thirdsource/drain electrode 1300. This copper layer 1400 may act as a seedlayer for growing copper nano-structures (particularly, nano-wires), asdescribed later.

Meanwhile, an oxide semiconductor based sol solution may be prepared inorder to form an oxide semiconductor layer (1500 of FIG. 11) using asol-gel process. The oxide semiconductor based sol solution used in thesol-gel process may be obtained by mixing compound dispersoidcorresponding to a source material of the oxide semiconductor in adispersion medium to form a disperse system, stirring the dispersesystem, and aging the stirred disperse system.

The compound dispersoid may include at least one selected from the groupconsisting of a zinc compound, an indium compound, a gallium compound, atin compound, a hafnium compound, a zirconium compound, a magnesiumcompound, an yttrium compound and a thallium compound. In particular,the dispersoid of the sol solution may include the zinc compound and anon-zinc compound. In this case, the dispersoid of the sol solution maybe formed by mixing the zinc compound and the non-zinc compound (e.g.,at least one of an indium compound, a gallium compound, a tin compound,a hafnium compound, a zirconium compound, a magnesium compound, anyttrium compound and a thallium compound) in a mole ratio of about 1:0.1to about 1:2. Further, a molar concentration of the zinc compound, theindium compound, the gallium compound, the tin compound, the hafniumcompound, the zirconium compound, the magnesium compound, the yttriumcompound or the thallium compound in the disperse system may be about0.1 mol/l (M) to about 10 mol/l (M).

The dispersion medium of the sol solution may include at least oneselected from the group consisting of isopropanol, 2-methoxyethanol,dimethylformamide, ethanol, de-ionized water, methanol, acetylacetone,dimethylamineborane and acetonitrile.

Specifically, the zinc compound used as the dispersoid of the solsolution may include at least one selected from the group consisting ofzinc citrate dihydrate, zinc acetate, zinc acetate dihydrate, zincacetylacetonate hydrate, zinc acrylate, zinc chloride, zincdiethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc fluoride,zinc fluoride hydrate, zinc hexafluoroacetylacetonate dihydrate, zincmethacrylate, zinc nitrate hexahydrate, zinc nitrate hydrate, zinctrifluoromethanesulfonate, zinc undecylenate, zinc trifluoroacetatehydrate, zinc tetrafluoroborate hydrate and zinc perchloratehexahydrate.

Further, the indium compound used as the dispersoid of the sol solutionmay include at least one selected from the group consisting of indiumchloride, indium chloride tetrahydrate, indium fluoride, indium fluoridetrihydrate, indium hydroxide, indium nitrate hydrate, indium acetatehydrate, indium acetylacetonate and indium acetate.

The gallium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of galliumacetylacetonate, gallium chloride, gallium fluoride and gallium nitratehydrate.

The tin compound used as the dispersoid of the sol solution may includeat least one selected from the group consisting of tin acetate, tinchloride, tin chloride dihydrate, tin chloride pentahydrate and tinfluoride.

The thallium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of thalliumacetate, thallium acetylacetonate, thallium chloride, thallium chloridetetrahydrate, thallium cyclopentadienide, thallium fluoride, thalliumformate, thallium hexafluoroacetylacetonate, thallium nitrate, thalliumnitrate trihydrate, thallium trifluroacetate and thallium perchloratehydrate.

The hafnium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of hafniumchloride and hafnium fluoride.

The magnesium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of magnesiumacetate, magnesium chloride, magnesium nitrate hydrate and magnesiumsulfate.

The zirconium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of zirconiumacetate, zirconium acetylacetonate, zirconium chloride and zirconiumfluoride.

The yttrium compound used as the dispersoid of the sol solution mayinclude at least one selected from the group consisting of yttriumacetate, yttrium acetylacetonate, yttrium chloride, yttrium fluoride andyttrium nitrate.

When the sol solution is formed, a sol stabilizer may be added to thedisperse system. The sol stabilizer may include mono-ethanolamine,di-ethanolamine or tri-ethanolamine. The sol stabilizer may be mixed tohave the same moles as the compound material of the dispersoid in thedisperse system.

Moreover, when the sol solution is formed, acid or base may be added tothe disperse system to adjust a potential of hydrogen (pH) of thedisperse system. For example, the potential of hydrogen (pH) of thedisperse system may be lowered if acetic acid (CH₃COOH) is added to thedisperse system, and the potential of hydrogen (pH) of the dispersesystem may be heightened if a base (e.g., ammonium hydroxide, potassiumhydroxide or sodium hydroxide) is added to the disperse system. Thus,the potential of hydrogen (pH) of the disperse system may beappropriately adjusted within the range of about 1 to 10 by adding theacid (e.g., acetic acid) or the base to the disperse system. In thepresent exemplary embodiment, the acid may be added to the dispersesystem such that the disperse system has the potential of hydrogen (pH)less than 7, and the acid component in the sol solution may be used ingrowth of the nano-structures in a subsequent process. Particularly, thepotential of hydrogen (pH) of the disperse system may be adjusted ofabout 3.8 to 4.2.

Referring to FIG. 11, the oxide semiconductor based sol solution (e.g.,zinc oxide based sol solution) prepared by the above method may beprovided on a surface of the gate insulation layer 1050 on the substrate1010 to form an oxide semiconductor layer 1500 of a first conductivitytype (an N-type in the present embodiment) on a portion of the gateinsulation layer 1050. This oxide semiconductor layer 1500 may be formedbetween the first and second source/drain electrodes 1100 and 1200 tocontact both the first and second source/drain electrodes 1100 and 1200.The oxide semiconductor layer 1500 may be formed by drying and heating asol solution provided on the gate insulation layer 1050 to transform thesol solution into an oxide semiconductor thin film through a gelledpattern.

An oxide semiconductor layer of a multi-component system may be formedaccording to appropriate selection of a disperse system in a step ofpreparing a sol solution, and various and diverse oxide semiconductorlayers may be formed by selecting a desired sol material. When thesol-gel process is used in formation of the oxide semiconductor thinfilm, various thin films having different compositions can be fabricatedwithin a short time and electrical characteristics of the thin films canbe easily controlled. Further, phases of the thin films can be easilychanged by varying temperature and/or process time of a thermaltreatment for transforming the sol solution into a gelled pattern. Theoxide semiconductor layer 1500 may be used as a semiconductor channelregion of the MOS transistors constituting the CMOS circuit, and acharacteristic of the semiconductor channel region may be varied bychanging the phase of the thin film or material as described above.

Referring to FIG. 12, acid may be supplied onto the copper layer 1400acting as a seed layer and a thermal treatment may be applied to thecopper layer 1400 on which the acid is supplied. As a result, copperoxide nano-structures, particularly, copper oxide (CuO) nano-wires 1600may be grown from the copper layer 1400. As illustrated in FIG. 12, thecopper oxide (CuO) nano-wires 1600 may be grown and at least some of thecopper oxide (CuO) nano-wires 1600 may be formed to contact the firstsource/drain electrode 1100. As such, the CuO nano-wires 1600 mayelectrically connect the copper layer 1400 to the first source/drainelectrode 1100, thereby acting as channels connecting the first andthird source/drain electrodes 1100 and 1300 to each other. Inparticular, since the grown CuO nano-wires 1600 correspond to P-typesemiconductors, the CuO nano-wires 1600 may act as P-channels betweenthe first and third source/drain electrodes 1100 and 1300. In contrast,the oxide semiconductor layer 1500 may correspond to an N-typesemiconductor. Thus, the oxide semiconductor layer 1500 may act as anN-channel between the first and second source/drain electrodes 1100 and1200. Accordingly, the device illustrated in FIG. 12 may be a CMOSdevice. That is, the first source/drain electrode 1100, the N-type oxidesemiconductor layer 1500 and the second source/drain electrode 1200 mayconstitute an N-channel MOSFET, and the third source/drain electrode1300, the P-type CuO nano-wires 1600 and the first source/drainelectrode 1100 may constitute a P-channel MOSFET.

As described above, if a thermal treatment is applied to the copperlayer 1400 after acid is supplied onto the copper layer 1400, P-type CuOnano-wires 1600 may be obtained from the copper layer 1400. The thermaltreatment for growth of the CuO nano-wires 1600 may be performed at atemperature of about 300° C. to about 1000° C. Further, the thermaltreatment for growth of the CuO nano-wires 1600 may be performed invacuum. The thermal treatment may be performed using at least one of anitrogen gas, a hydrogen gas and an oxygen gas as an ambient gas. Assuch, the CuO nano-wires 1600, which are grown by a thermal treatmentapplied to the copper layer with acid, may be formed to be self-alignedwith desired positions even without use of complicated processes such asseparation, refinement and arrangement of the nano-structures. That is,the at least some of the CuO nano-wires 1600 may be grown from thecopper layer 1400 to contact the first source/drain electrode 1100.Thus, according to the present embodiment, the nano-structures may beformed at desired positions even without use of a photolithographyprocess. The nano-structures (corresponding to the CuO nano-wires in thepresent embodiment), which are grown by a thermal treatment applied tothe copper layer with acid, may not include any catalyst componentsremained at ends thereof. That is, the nano-structures according to thepresent embodiment may not be contaminated with any metal catalysts,unlike the nano-structures fabricated using a catalyst. Thus, it may bepossible to apply single crystalline pure nano-structures withoutcontamination to electronic devices.

In the present embodiment described above, the acid supplied onto thecopper layer 1400 for growth of the CuO nano-wires may be provided inthe form of sol solution having a pH less than 7. In this case, whilethe sol solution is gelled, the N-type oxide semiconductor layer 1500and the CuO nano-wires 1600 may be simultaneously formed. That is, theoxide semiconductor based sol solution containing acid may be providedonto a portion of the gate insulation layer 1050 (between the first andsecond source/drain electrodes 1100 and 1200) as well as the copperlayer 1400. Subsequently, the sol solution may be gelled using a thermaltreatment, thereby forming the N-type oxide semiconductor layer 1500 onan N-channel region between the first and second source/drain electrodes1100 and 1200 as well as the CuO nano-wires 1600 extending from thecopper layer 1400 onto the first source/drain electrode 1100. The phaseof the oxide semiconductor layer 1500 and/or the sizes, lengths orelectrical characteristics of the CuO nano-wires 1600 may be controlledby changing the temperature and process time of the thermal treatment.

The above exemplary embodiment is described in conjunction with CMOSdevices and fabrication processes thereof. However, the inventiveconcept is not limited to the CMOS devices and fabrication processthereof. For example, the inventive concept may be applied to MOSFETs,PN junction diodes, JFETs or the like.

FIG. 13 illustrates an oxide semiconductor device 2000 including a CuOnano-structure according to another exemplary embodiment. Referring toFIG. 13, the oxide semiconductor device 2000 may include a CuO nano-wire2010 having a P-type semiconductor and an N-type oxide semiconductorlayer 2030 surrounding an outer circumference of the nano-wire 2010. Theoxide semiconductor device 2000 may have a P-N junction formed by theP-type nano-wire 2010 and the N-type oxide semiconductor layer 2030. TheCuO nano-wire 2010 may be obtained through the chemical reaction of thecopper layer on the acid and the thermal treatment applied to the copperlayer, as described above. Further, the N-type oxide semiconductor layer2030 may be obtained by transforming the oxide semiconductor based solsolution into a gelled material. That is, the N-type oxide semiconductorlayer 2030 may be obtained by supplying a sol solution onto the outercircumference of the nano-wire 2010 and heating the sol solution to forma thin film having an N-type semiconductor property. As a result, theN-type oxide semiconductor layer 2030 and the P-type nano-wire 2010 mayconstitute a diode having a P-N junction.

The oxide semiconductor device 2000 illustrated in FIG. 13 may be usedas a P-N diode. Further, in the event that additional electrodes areformed on the oxide semiconductor device 2000, a JFET can be obtained(refer to FIG. 14). Moreover, the fabrication process of the oxidesemiconductor device 2000 may be used in growth of CuO nano-structuresdistributed on a substrate having a large area and in deposition of thinfilms using a sol-gel process. That is, the fabrication process of theoxide semiconductor device 2000 may be used in formation of solar cells.

FIGS. 14A and 14B illustrate an oxide semiconductor device 3000including CuO nano-structures fabricated according to yet anotherexemplary embodiment. FIG. 14A is a cross sectional view illustratingthe oxide semiconductor device 3000, and FIG. 14B is a cross sectionalview illustrating operation principles of the oxide semiconductor device3000.

Referring to FIG. 14A, the oxide semiconductor device 3000 may include aP-type CuO nano-wire 3010, an N-type oxide semiconductor layer 3030surrounding an outer surface of the P-type CuO nano-wire 3010,source/drain electrodes 3020 formed on both ends of the P-type CuOnano-wire 3010, and a gate electrode 3050 formed on the N-type oxidesemiconductor layer 3030. This oxide semiconductor device 3000 may actas one of JFETs. That is, the oxide semiconductor device 3000 mayoperate as a transistor.

Referring to FIG. 14B, a width of a depletion region 3010 a formed inthe P-type CuO nano-wire 3010 may be adjusted according to a voltage(e.g., a gate voltage) applied to the gate electrode 3050. The width ofa depletion region 3010 a may control a cross sectional area of aneffective channel region corresponding to the central region of the CuOnano-wire 3010, which is surrounded by the depletion region 3010 a.Thus, a current flowing through the effective channel region between thesource/drain electrodes 3020 may be controlled by the gate voltage.

FIG. 15 is a scanning electron microscope (SEM) picture illustratingcopper oxide (CuO) nano-wires grown through a chemical reaction ofcopper on acid and thermal treatment applied to the copper. The CuOnano-wires illustrated in FIG. 15 are P-type semiconductors that can beapplied to an oxide semiconductor device fabricated according to anexemplary embodiment. The CuO nano-wires grown from a copper grid mayhave a diameter of about several hundred nanometers and a length ofabout several hundred nanometers to several micrometers. The CuOnano-wires may be formed without any contamination due to metalcatalysts, unlike the nano-structures fabricated using a metal catalyst.That is, the CuO nano-wires may be formed to have pure semiconductornano-structures without metal components bonded to ends of thenano-structures. Thus,

<Methods of Fabricating an Oxide Nano-Structure Using a Sol-Gel Processand a Porous Nano-Structure>

Various nano-structures may be formed using a vapor-liquid-solid (VLS)mechanism, a vapor-solid (VS) mechanism, a solution-liquid-solid (SLS)mechanism or the like.

A metal catalyst may be required to fabricate the nano-structures usingthe VLS mechanism, and the metal catalyst may include metal (e.g., gold(Au), nickel (Ni) or iron (Fe)), which is capable of lowering a meltingpoint of a material. In this VLS mechanism, the position and the size ofthe catalyst may control the position and the diameter of thenano-structures. The nano-structures fabricated using the VLS mechanismmay have a high quality of crystallinity.

For instance, a typical prior art for obtaining a silicon nano-structureusing the VLS mechanism is disclosed in an article (a first referencearticle) by Lincoln J. Lauhon et al., entitled “Expitaxial core-shelland core-multishell narrowire heterostructures”, Nature 420, 57 (2002).According to the first reference article, gaseous reactants may becombined with gold (on gold nano-cloud surfaces) acting as catalysts togenerate nuclei and the nuclei may grow to form silicon nano-structureshaving a multi shell

While the silicon nano-structures are formed, the gold may act as acatalyst. The gold may lower a melting point of silicon so that the goldand the silicon are easily alloyed with each other in a liquid state.This can be seen from a phase diagram of silicon and iron (Fe). That is,if a metal catalyst is used in fabrication of nano-structures, the metalcatalyst may remain at ends of the nano-structures. This may correspondto a method of forming nano-structures using the VLS mechanism.

The VLS mechanism described above may be a typical method used not onlyin formation of the silicon nano-structure but also in formation of aone dimensional nano-structure such as Ge, ZnO, ZnSe, GaAs, GaP, GaN,InP, CdS or CdSe (refer to a second reference article by Younan Xia etal., entitled “One Dimensional Nano-structures: Synthesis,Characterization, and Application”, Advanced Material, 15, 353 (2003)).

Meanwhile, in order to fabricate nan-structures using the SLS mechanism,a liquid precursor and a catalyst such as gold may be required. The goldacting as the catalyst may increase overall yield of the nano-structuresor may control the diameter and the location of the nano-structures.That is, the nano-structures fabricated using the SLS mechanism may begrown at a relatively low temperature as compared with thenano-structures fabricated using the VLS mechanism. Thus, thecrystallinity of the nano-structures fabricated using the SLS mechanismmay be degraded as compared with the crystallinity of thenano-structures fabricated using the VLS mechanism.

For instance, a typical prior art for obtaining a silicon nano-structureusing the SLS mechanism is disclosed in an article (a third referencearticle) by Xianmao Lu et al., entitled “Growth of Single CrystalSilicon Narrowires in Supercritical Sliution from Tethered GoldParticles on a Silicon Substrate”, Nano letters, 3, 93 (2003). Accordingto the third reference article, gold nano-particles, (C₆H₅)₂SiH₂ andhexane may be used as a metal catalyst, a silicon liquid precursor and asolvent, respectively. In this case, the (C₆H₅)₂SiH₂ may be decomposedinto silicon atoms and the silicon atoms may be alloyed with the goldnano-particles in a liquid state to extract silicon. As a result,silicon nano-structures may be formed. The metal catalyst may controlthe diameter of the nano-structures and may control the location of thenano-structures.

Meanwhile, the conventional method of fabricating a zinc oxidenano-structure will now be described. This conventional method may beperformed using a metal catalyst, a sol-gel process without a vapor, andan extraction technique. Specifically, zinc nitrate is dissolved inde-ionized water to form a zinc nitride solution, and ammonium carbideis dissolved in de-ionized water to form an ammonium carbide solution.The zinc nitride solution may be slowly dropped onto the ammoniumcarbide solution and the mixture may be stirred to extract. Theextracted material may be filtered and rinsed using de-ionized water toremove remnants. Subsequently, the resultant may be again dipped intode-ionized water and stirred for about five minutes. The floatingmaterials may be put in a Teflon-lined autoclave having a capacity of100 milli-liters and a hydrothermal synthesis may be performed fromabout 130° C. to about 200° C. Subsequently, the resultant may be rinsedusing alcohol and may be dried at a temperature of about 90° C. fortwelve hours to obtain a zinc oxide nano-structure.

The other conventional method of fabricating a zinc oxide nano-structurewill now be described. According to this conventional method, alignedzinc oxide nano-structures may be formed using an anodic aluminum oxide(AAO) material. Specifically, AAO porous nano-structures are formed, andcontaminants and a barrier layer are removed using an HgCl₂ solution anda phosphoric acid solution. Gold may be then deposited on the AAO usinga sputtering process. Growth of nano-structures may be performed in atube furnace. The AAO porous nano-structures may be coated by zinc.Subsequently, a thermal treatment may be performed at a temperature ofabout 800° C. to about 900° C. using an argon gas as an ambient gas,thereby completely evaporating the zinc. Finally, performance of thethermal treatment and injection of the argon gas are stopped, and anoxygen gas is then injected to form zinc oxide nano-structures.

However, according to the aforementioned prior arts, the nano-structuresare formed using a deposition process with a high priced vacuumapparatus and a catalyst. Thus, the fabrication process may becomecomplicated and the fabrication cost may be increased.

Accordingly, the exemplary embodiments provide methods of fabricating anoxide nano-structure by injecting an oxide material into a porousnano-structure using a sol-gel process. Thus, a metal oxide material ofa multi-component system may be efficiently formed, and the oxidenano-structure may be formed to have a desired composition, a desiredsize and a desired phase.

The exemplary embodiment provides a method of fabricating metal oxidesemiconductor nano-structures of a multi-component system using asol-gel process and a porous template.

The exemplary embodiment may include a step of fabricating a solmaterial, a step of fabricating a porous template, a step of applying asurface treatment to the porous template, and a step of injecting anoxide material solution (e.g., a liquid oxide compound sol material)into the surface treated porous template. Subsequently, a thermaltreatment may be performed and the porous template may be removed toform oxide nano-structures.

Composition of the nano-structures may be determined according tocomposition of the sol material, and the size of the oxidenano-structures may be adjusted according to a shape and a size of theporous template. Further, the shape of the oxide nano-structures may bedetermined according to a process condition of the surface treatmentapplied to the porous template. The phase of the nano-structures may bedetermined according to a temperature of the thermal treatment.According to the exemplary embodiment, oxide nano-structures of amulti-component system may be easily formed using a simplified process,and the size, shape and phase of the oxide nano-structures can be easilycontrolled.

That is, one of the features of the exemplary embodiments is to injectan oxide material solution into a porous nano-structure using a sol-gelprocess. Thus, the exemplary embodiments may be distinguished from amethod of fabricating a nano-structure using a deposition process with avacuum apparatus and a catalyst.

FIGS. 16 to 19 are schematic drawings illustrating a method of formingoxide nano-structures using a porous nano-structure and a sol-gelprocess according to an exemplary embodiment.

Referring to FIG. 16, a substrate 500 having a porous template, forexample, porous nano-structures P may be provided. A surface treatmentmay be applied to the substrate 500 using a physical method or achemical method. The substrate 500 having the porous nano-structures Pmay preferably include an anodic aluminum oxide (AAO) material or anacrylamide (AAM) material.

The chemical method utilized as the surface treatment may be performedusing a chemical solution, for example, a piranha solution, a mixture ofde-ionized water and acetone, a toluene material or anoctadecyltetrachlorosilane-self-assembled-monolayers (OTS-SAMs)material. Surfaces of the porous nano-structures P treated by any one ofthe above listed chemical solutions may have viscosity to a metal oxidesolution of a multi-component system. Thus, the metal oxide solution maybe easily injected into the porous nano-structures P in a subsequentprocess. The physical method may be performed by stirring the chemicalsolution or applying an ultrasonic process to the substrate togetherwith the chemical solution.

For instance, before a metal oxide solution such as a liquid oxidecompound sol solution (600 of FIG. 17) is injected into the porousnano-structures P including the anodic aluminum oxide (AAO) material,the surface treatment may be applied to the substrate having the porousnano-structures P. The surface treatment may allow the liquid oxidecompound sol solution 600 to be smoothly injected into the porousnano-structures P. That is, if the surface treatment is not performedsuccessfully, the liquid oxide compound sol solution 600 may not besmoothly injected into the porous nano-structures P. It is preferablethat the surface treatment is applied to the porous nano-structures Pusing an appropriate chemical reaction for an appropriate process time.

Referring to FIG. 17, the oxide compound sol solution 600 may beinjected into the surface treated porous nano-structures P. For example,an In—Ga—ZnO (IGZO) solution corresponding to the oxide compound solsolution 600 may be injected into the surface treated anodic aluminumoxide (AAO) porous nano-structures P. The IGZO solution may bepreferably injected using a dip coating method. However, the method ofinjecting the IGZO solution is not limited to the dip coating method.For example, the IGZO solution may be injected using a spin coatingmethod.

If the IGZO solution is injected using the spin coating method after thesurface treatment, the IGZO solution may be deposited only on a topsurface of substrate 500 and may not be injected into the porousnano-structures P. This may be due to centrifugal force which isgenerated by rotation of the substrate during the spin coating process.This effect may still cause even though the spin coating process isperformed with low revolutions per minute (RPM) thereof.

However, in the event that the RPM of the spin coating process is verylow, the IGZO solution may be injected into the porous nano-structures Pbecause the centrifugal force applied to the IGZO solution is remarkablyreduced. However, in an exemplary embodiment, the IGZO solution may beinjected into the porous nano-structures P using a dip coating process.The dip coating process may be performed by dipping the substrateincluding the surface treated anodic aluminum oxide (AAO) porousnano-structures P into a vessel filled with the IGZO solution.

The important parameters of the dip coating process may be anatmospheric pressure and a process temperature. For example, the dipcoating process may be performed at a temperature of about 100° C. invacuum. Preferably, the oxide compound sol solution 600 may be injectedinto the porous nano-structures P at a temperature of about 80° C. toabout 100° C. under a vacuum condition of about 1×10⁻¹ torr to about1×10⁻⁷ torr.

In the dip coating process, creating the temperature of about 100° C. isfor increasing the viscosity of the substrate surface to the IGZOsolution below a temperature at which the IGZO solution loses its ownproperty, and creating the vacuum condition is for removing air in theanodic aluminum oxide (AAO) porous nano-structures P to smoothlyinjecting the IGZO solution into the porous nano-structures P withoutany voids. That is, the dip coating process may be performed using acapillary phenomenon. Thus, the oxide nano-structures injected into theporous nano-structures P may have a uniform size and composition.

In the meantime, the oxide compound sol solution 600 may be formed bymixing dispersoid in the corresponding dispersion medium to form adisperse system, stirring the disperse system, and aging the stirreddisperse system. The dispersoid may include at least two compoundmaterials selected from the group consisting of a zinc compound, anindium compound, a gallium compound, a tin compound, a hafnium compound,a zirconium compound, a magnesium compound, an yttrium compound and athallium compound. The dispersoid may be formed by mixing the zinccompound and a non-zinc compound (e.g., at least one of the indiumcompound, the gallium compound, the tin compound, the hafnium compound,the zirconium compound, the magnesium compound, the yttrium compound andthe thallium compound) in a mole ratio of about 1:0.1 to about 1:2.

The dispersion medium may include at least one selected from the groupconsisting of isopropanol, 2-methoxyethanol, dimethylformamide, ethanol,de-ionized water, methanol, acetylacetone, dimethylamineborane andacetonitrile.

The zinc compound may include at least one selected from the groupconsisting of zinc citrate dihydrate, zinc acetate, zinc acetatedihydrate, zinc acetylacetonate hydrate, zinc acrylate, zinc chloride,zinc diethyldithiocarbamate, zinc dimethyldithiocarbamate, zincfluoride, zinc fluoride hydrate, zinc hexafluoroacetylacetonatedihydrate, zinc methacrylate, zinc nitrate hexahydrate, zinc nitratehydrate, zinc trifluoromethanesulfonate, zinc undecylenate, zinctrifluoroacetate hydrate, zinc tetrafluoroborate hydrate and zincperchlorate hexahydrate.

Further, the indium compound may include at least one selected from thegroup consisting of indium chloride, indium chloride tetrahydrate,indium fluoride, indium fluoride trihydrate, indium hydroxide, indiumnitrate hydrate, indium acetate hydrate, indium acetylacetonate andindium acetate.

The gallium compound may include at least one selected from the groupconsisting of gallium acetylacetonate, gallium chloride, galliumfluoride and gallium nitrate hydrate.

The tin compound may include at least one selected from the groupconsisting of tin acetate, tin chloride, tin chloride dihydrate, tinchloride pentahydrate and tin fluoride.

The thallium compound may include at least one selected from the groupconsisting of thallium acetate, thallium acetylacetonate, thalliumchloride, thallium chloride tetrahydrate, thallium cyclopentadienide,thallium fluoride, thallium formate, thallium hexafluoroacetylacetonate,thallium nitrate, thallium nitrate trihydrate, thallium trifluroacetateand thallium perchlorate hydrate.

Further, a molar concentration of the zinc compound, the indiumcompound, the gallium compound, the tin compound or the thalliumcompound in the disperse system may be about 0.1 mol/l (M) to about 10mol/l (M).

When the sol solution is formed, a sol stabilizer may be added to thedisperse system. The sol stabilizer may be added to have the same molesas the zinc compound material. The sol stabilizer may include at leastone of mono-ethanolamine, di-ethanolamine and tri-ethanolamine.

Moreover, when the sol solution is formed, acid or base may be added tothe disperse system to adjust a potential of hydrogen (pH) of thedisperse system. For example, the potential of hydrogen (pH) of thedisperse system may be lowered if acetic acid (CH₃COOH) is added to thedisperse system, and the potential of hydrogen (pH) of the dispersesystem may be heightened if a base (e.g., ammonium hydroxide, potassiumhydroxide or sodium hydroxide) is added to the disperse system. Thus,the potential of hydrogen (pH) of the disperse system may beappropriately adjusted within the range of about 1 to 10 by adding theacid (e.g., acetic acid) or the base to the disperse system. Morepreferably, the potential of hydrogen (pH) of the disperse system may beadjusted of about 3.8 to 4.2.

Referring to FIG. 18, the oxide compound sol solution 600 injected intothe porous nano-structures P may be dried and heated using a thermaltreatment process to transform the oxide compound sol solution 600 intogelled patterns. As a result, oxide nano-structures 700 may be formed inrespective ones of the porous nano-structures P. Preferably, the thermaltreatment process may be performed at a temperature of about 300° C. toabout 1000° C.

For instance, the thermal treatment process for curing the oxidecompound sol solution 600 may be performed using an oxygen gas as anambient gas.

FIG. 20 is a merged drawing including a TG (thermo-gravimetricanalysis)-DSC (differential scanning calorimetry) measurement graph ofan IGZO solution and transmission electron microscope (TEM) pictures ofphases of IGZO materials cured at various temperatures. In the IGZOsolution, a composition ratio of indium, gallium and zinc was 1:1:2.

Referring to FIG. 20, the dispersion medium, i.e., a solvent may bedecomposed at a temperature lower than about 150° C., and the decomposedelements may be combined with each other at a temperature of about 200°C. to form an oxide compound material. Further, the oxide compoundmaterial, i.e., the IGZO material may be crystallized at a temperaturewithin the range of about 305° C. to about 420° C. Three TEM pictures inFIG. 20 illustrate phases of IGZO materials cured at temperatures of300° C., 400° C. and 500° C., respectively.

As can be seen from the TEM pictures, the IGZO materials had a phasecorresponding to an amorphous state at a temperature below thecrystallization temperature and a phase corresponding to apolycrystalline state at a temperature over the crystallizationtemperature. Thus, the TEM pictures were consistent with the TG-DSCmeasurement results illustrated in the graph. The TG-DSC measurementresults were hardly changed even though the composition ratio of theIGZO material was varied. The IGZO nano-structures may be obtainedthrough the curing process, for example, a thermal treatment process.

As described in the above exemplary embodiment, the oxidenano-structures may be obtained by injecting the oxide materialsolution, for example, the oxide compound sol solution 600 into theanodic aluminum oxide (AAO) porous nano-structures P. This method mayhave advantages which are capable of obtaining the nano-structures usinga metal oxide solution of a multi-component system and capable of easilychanging the size and shape of the nano-structures according to theprocess condition of the anodic aluminum oxide (AAO). Further, asillustrated in FIG. 20, the phase of the oxide nano-structures formed inthe anodic aluminum oxide (AAO) porous nano-structures P may be changedby controlling the curing temperature. Furthermore, the nano-structuresmay be formed to have a desired composition by changing a composition ofan oxide material solution during fabrication of the oxide materialsolution.

Referring to FIG. 19, the oxide nano-structures 700 and the porousnano-structures P may be separated from each other. The separation ofthe oxide nano-structures 700 and the porous nano-structures P mayinclude etching the porous nano-structures P using an etchant such as asodium hydroxide solution and obtaining the oxide nano-structures 700using a centrifugal separation process.

In the meantime, shapes of the oxide nano-structures 700 may bedetermined by shapes of the porous nano-structures P. For example, theoxide nano-structures 700 may be formed to have a dot shape or acylindrical shape, and the oxide nano-structures 700 may be formed tohave a size of about several nanometers to about several micrometers.

While the inventive concept has been described with reference to exampleembodiments, it will be apparent to those skilled in the art thatvarious changes and modifications may be made without departing from thespirit and scope of the inventive concept. Therefore, it should beunderstood that the above embodiments are not limiting, butillustrative. Thus, the scope of the inventive concept is to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing description.

INDUSTRIAL APPLICABILITY

The exemplary embodiments of the inventive concept may be applied tomethods of fabricating electronic devices, thin film transistors (TFTs),liquid crystal display devices employing the TFTs, memory transistors ormemory devices with a sol-gel process.

What is claimed is:
 1. A method of fabricating an oxide semiconductordevice, comprising: forming a gate electrode layer on a substrate;forming a gate insulation layer on the gate electrode layer; formingfirst, second and third source/drain electrodes on the gate insulationlayer, and the first source/drain electrode is formed between the secondand third source/drain electrodes; forming a semiconductor layer of afirst conductivity type on the gate insulation layer between the firstand second source/drain electrodes to act as a channel region thatconnects the first source/drain electrode to the second source/drainelectrode; forming a copper layer on the third source/drain electrode;and forming a copper oxide nano-structure of a second conductivity grownfrom the copper layer to contact the first source/drain electrode. 2.The method of claim 1, wherein the forming the copper oxidenano-structure of the second conductivity includes supplying acid ontothe copper layer and applying a thermal treatment to the copper layer.3. The method of claim 1, wherein forming the semiconductor layer of thefirst conductivity type includes preparing an oxide semiconductor basedsol solution.
 4. The method of claim 2, wherein the thermal treatment isperformed at a temperature of about 300° C. to about 1000° C.
 5. Themethod of claim 4, wherein the thermal treatment is performed in avacuum or using at least one of a nitrogen gas, a hydrogen gas and anoxygen gas as an ambient gas.
 6. The method of claim 1, whereinpreparing the oxide semiconductor based sol solution includes mixing atleast one dispersoid selected from the group consisting of a zinccompound, an indium compound, a gallium compound, a tin compound, ahafnium compound, a zirconium compound, a magnesium compound, an yttriumcompound and a thallium compound in a dispersion medium corresponding tothe selected dispersoid to form a disperse system.
 7. The method ofclaim 6, wherein the dispersoid is formed by mixing the zinc compoundand at least one non-zinc compound selected from the group consisting ofm the indium compound, the gallium compound, the tin compound, thehafnium compound, the zirconium compound, the magnesium compound, theyttrium compound and the thallium compound in a mole ratio of about1:0.1 to about 1:2; and wherein the dispersion medium includes at leastone selected from the group consisting of isopropanol, 2-methoxyethanol,dimethylformamide, ethanol, de-ionized water, methanol, acetylacetone,dimethylamineborane and acetonitrile.
 8. The method of claim 6, whereina molar concentration of the zinc compound, the indium compound, thegallium compound, the tin compound, the hafnium compound, the zirconiumcompound, the magnesium compound, the yttrium compound or the thalliumcompound in the disperse system is about 0.1 mol/l (M) to about 10 mol/l(M).
 9. An oxide semiconductor device comprising: a gate electrode layerformed on a substrate; a gate insulation layer formed on the gateelectrode layer; first, second and third source/drain electrodes formedon the gate insulation layer, the first source/drain electrode beingdisposed between the second and third source/drain electrodes; asemiconductor layer of a first conductivity type formed on the gateinsulation layer between the first and second source/drain electrodes toact as a channel region that connects the first source/drain electrodeto the second source/drain electrode; a copper layer formed on the thirdsource/drain electrode; and a copper oxide nano-structure of a secondconductivity type grown from the copper layer to contact the firstsource/drain electrode.
 10. The oxide semiconductor device of claim 9,wherein the oxide semiconductor device is a complementarymetal-oxide-semiconductor (CMOS) device.